Golf ball paint composition

ABSTRACT

A golf ball paint composition includes primarily a urethane paint containing polyol as a base resin and polyisocyanate as a curing agent. The polyisocyanate includes two types of isocyanurate and adduct of hexamethylene diisocyanate and the golf ball paint composition has an elastic work recovery of at least 70%. The paint composition has a high self-repairing ability and is of high quality as a golf ball paint. Golf balls coated with this composition are able to maintain a good durability, in addition to which they have an excellent abrasion resistance and an excellent ball appearance.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending application Ser.No. 15/807,736 filed on Nov. 9, 2017, the entire contents of which arehereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a paint composition for golf balls.

BACKGROUND ART

The surface portion of a golf ball is often coated with a paintcomposition in order to protect the ball surface or to maintain anattractive appearance. Two-part curing polyurethane paints which areused by mixing together a polyol and a polyisocyanate just prior toapplication are suitably employed as such golf ball paint compositionsfor a number of reasons, including their ability to withstand largedeformation, impact and abrasion (see, for example, JP-A 2003-253201).

A frequent aim of recent golf ball development has been to further lowerthe spin rate on full shots taken with a driver. This move toward lowerspin rates has engendered a trend toward greater softness in the coverserving as the outermost layer of the ball.

Most golf balls have a core, a cover positioned outside of the core, anda paint film layer positioned outside of the cover. Making this paintfilm layer soft also often provides certain advantages, such ascontributing to stability in the spin rate of the golf ball andimparting outstanding durability (see, for example, JP-A 2011-67595).Additional related art is described in JP-A 2002-53799.

Golf ball paints which use one type of polyester polyol alone as thepolyol component have also been developed.

However, the surface of the paint film layer lacks a good abrasionresistance, and so there is room for further improvement.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a golf ball paintcomposition which can increase the abrasion resistance of the paintfilm.

As a result of extensive investigations, the inventor has discoveredthat, with regard to paint compositions in which the chief component isa urethane paint composed of polyol and polyisocyanate, by using twotypes of isocyanurate being hexamethylene diisocyanate havingcomparatively tough characteristics and adduct of hexamethylenediisocyanate having improved softness, and by also preparing the paintcomposition such that it has an elastic work recovery of at least 70%,paint films obtained from this paint composition have softness andnon-yellowing properties, enabling the spin rate to be improved for agolf ball.

Accordingly, the invention provides a golf ball paint compositioncomprising a urethane paint containing polyol as a base resin andpolyisocyanate as a curing agent, wherein the polyisocyanate includestwo types of isocyanurate and adduct of hexamethylene diisocyanate andthe composition has an elastic work recovery of at least 70%.

The composition of the invention has an elastic work recovery ofpreferably at least 80%.

In the paint composition of the invention, the compounding ratio byweight ratio of the isocyanurate (A) to the adduct (B) of hexamethylenediisocyanate, expressed as (A)/(B), is preferably from 95/5 to 40/60.

Also, in the paint composition of the invention, the polyol includes oneor two types of polyester polyol.

Secondly, the invention provides a golf ball having a core, a coverpositioned outside of the core, and a paint film layer positionedoutside of the cover wherein the paint film layer is formed of the abovepaint composition of the first invention.

In the golf ball of the invention, a cover composition forming the coverhas an elastic work recovery of at least 35%.

Also, in the golf ball of the invention, letting an elastic workrecovery of the paint film be W1 and letting an elastic work recovery ofthe cover be W2, the difference W1−W2 between the elastic work recoveryof the paint film and the elastic work recovery of the cover is at most40%.

Advantageous Effects of the Invention

The golf ball paint composition of the invention has a high elasticityand thus a high self-repairing ability, giving it a high abrasionresistance as a golf ball paint. Moreover, the paint composition is ableto enhance the performance of golf balls painted therewith.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The objects, features and advantages of the invention will become moreapparent from the following detailed description.

The golf ball paint composition of the invention is composed primarilyof a urethane paint made up of polyol and polyisocyanate.

One or two types of polyester polyol are used as the polyol in the baseresin. In the case of two types of polyester polyol, the polyols includepolyester polyol (A) and polyester polyol (B). These two types ofpolyester polyol have different weight-average molecular weights (Mw),with the Mw of polyester polyol (A) being preferably from 20,000 to30,000 and the Mw of polyester polyol (B) being preferably from 800 to1,500. The Mw of polyester polyol (A) is more preferably from 22,000 to29,000, and even more preferably from 23,000 to 28,000. The Mw ofpolyester polyol (B) is more preferably from 900 to 1,200, and even morepreferably from 1,000 to 1,100.

These two types of polyester polyol can be obtained by thepolycondensation of a polyol with a polybasic acid. Illustrativeexamples of the polyol include diols such as ethylene glycol,1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol,1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol,hexylene glycol, dimethylol heptane, polyethylene glycol andpolypropylene glycol; triols, tetraols, and polyols having an alicyclicstructure. Illustrative examples of polybasic acids include aliphaticdicarboxylic acids such as succinic acid, adipic acid, sebacic acid,azelaic acid and dimer acid; aliphatic unsaturated dicarboxylic acidssuch as fumaric acid, maleic acid, itaconic acid and citraconic acid;aromatic polycarboxylic acids such as phthalic acid, isophthalic acid,terephthalic acid, trimellitic acid and pyromellitic acid; dicarboxylicacids having an alicyclic structure, such as tetrahydrophthalic acid,hexahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid,1,4-cyclohexanedicarboxylic acid and endomethylenetetrahydrophthalicacid; and tris-2-carboxyethyl isocyanurate. In particular, polyesterpolyols in which cyclic structures have been introduced onto the resinskeleton may be used as polyester polyol (A). Examples include polyesterpolyols obtained by the polycondensation of a polyol having an alicyclicstructure, such as cyclohexane dimethanol, with a polybasic acid; andpolyester polyols obtained by the polycondensation of a polyol having analicyclic structure with a diol or triol and a polybasic acid. Polyesterpolyols which have a multi-branched structure may be used as polyesterpolyol (B). Examples include polyester polyols having a branchedstructure, such as NIPPOLAN 800 from Tosoh Corporation.

The weight-average molecular weight (Mw) of the overall base resin madeof these two types of polyester polyols is preferably from 13,000 to23,000, and more preferably from 15,000 to 22,000. The number-averagemolecular weight (Mn) of the overall base resin made of these two typesof polyester polyols is preferably from 1,100 to 2,000, and morepreferably from 1,300 to 1,850. At average molecular weights (Mw and Mn)outside of these ranges, the abrasion resistance of the paint film maydecrease. The weight-average molecular weight (Mw) and number-averagemolecular weight (Mn) are polystyrene equivalent values measured by gelpermeation chromatography (GPC) using a differential refractometer.

Although the contents of the two types of polyester polyol (A) and (B)are not particularly limited, based on the overall amount of base resin,the content of polyester polyol (A) is preferably from 20 to 30 wt % andthe content of polyester polyol (B) is preferably from 2 to 18 wt %.

When only one kind of polyester polyol is used in the golf ball paintcomposition of the invention, it is preferable that the type ofpolyester polyol is the polyester polyol (A) described above.

The polyisocyanate used in this invention includes two types ofisocyanurate and adduct of hexamethylene diisocyanate.

The polyisocyanate used in this invention includes two types ofisocyanurate and adduct of hexamethylene diisocyanate. The hexamethylenediisocyanate includes modified forms of hexamethylene diisocyanate, forexample, polyester-modified hexamethylene diisocyanate andurethane-modified hexamethylene diisocyanate. The hexamethylenederivatives of hexamethylene diisocyanate including the biuret togetherwith the isocyanurate and adduct of hexamethylene diisocyanate.

In the paint composition of the invention, the compounding ratio byweight ratio of the isocyanurate (A) to the adduct (B) of hexamethylenediisocyanate, expressed as (A)/(B), is preferably from 95/5 to 40/60,more preferably 80/20 to 55/45.

Isocyanurate of hexamethylene diisocyanate (HMDI) may be a commerciallyavailable products. Examples of such isocyanurate of hexamethylenediisocyanate (HMDI) include “Coronate 2357” (Tosoh Corporation),“Sumidule N3300” (Sumitomo Covestro Urethane Co., Ltd.), “DuranateTPA-100” (Asahi KASEI Corporation), “Takenate D170N”, “Takenate D177N”(all of Mitsui Chemicals Corporation) and “Burnock DN-980” (all of DICCorporation). These may be used singly, or two or more may be usedtogether. Adducts of hexamethylene diisocyanate (HMDI) may be acommercially available products. Examples of such isocyanurate ofhexamethylene diisocyanate (HMDI) include “Coronate HL” (TosohCorporation), “Takenate D160N” (Mitsui Chemicals Corporation), “DuranateE402-80B”, “Duranate E405-70B” (all of Asahi KASEI Corporation) and“Burnock DN-955”, “Burnock DN-955S” (all of DIC Corporation). These maybe used singly, or two or more may be used together.

The compounding ratio by weight ratio of the isocyanurate (A) to theadduct (B) of hexamethylene diisocyanate, expressed as (A)/(B), ispreferably from 95/5 to 40/60 and more preferably from 80/20 to 55/45.

The molar ratio of isocyanate (NCO) groups on the polyisocyanate tohydroxyl (OH) groups on the polyester polyol used in the invention,expressed as NCO/OH, is preferably at least 0.6, and more preferably atleast 0.65, and is preferably not more than 1.5, more preferably notmore than 1.0, and even more preferably not more than 0.9. When thismolar ratio falls below the above lower limit, unreacted hydroxyl groupsremain, which may worsen the performance and water resistance as a golfball paint film. On the other hand, when the molar ratio exceeds theabove upper limit, because the number of isocyanate groups becomesexcessive, urea groups (which are fragile) form in reactions withmoisture, as a result of which the golf ball paint film performance maydecline.

An amine catalyst or an organometallic catalyst may be used as thecuring catalyst (organometallic compound). Examples of suchorganometallic compounds include soaps of metals such as aluminum,nickel, zinc or tin. Preferred use can be made of those which havehitherto been formulated as curing agents for two-part curing urethanepaints.

Known paint compounding ingredients may be optionally added to the golfball paint composition. For example, thickeners, ultraviolet absorbers,fluorescent brighteners, slip agents and pigments may be included insuitable amounts.

The golf ball paint composition has an elastic work recovery that mustbe at least 70%, and is preferably at least 80%. When the elastic workrecovery of the inventive paint composition falls outside of this range,the abrasion resistance may worsen. In this invention, because the paintfilm that forms on the golf ball surface has a high elasticity, theself-recovery ability is high, resulting in an outstanding abrasionresistance. Moreover, various performance attributes of the golf ballscoated with this paint composition can be improved. The method ofmeasuring the elastic work recovery of the golf ball paint compositionis described later in this specification.

The elastic work recovery is one parameter of the nanoindentation methodfor evaluating the physical properties of paint films, which is ananohardness test method that controls the indentation load on amicro-newton (μN) order and tracks the indenter depth during indentationto a nanometer (nm) precision. In prior methods, only the size of thedent (plastic deformation) corresponding to the maximum load could bemeasured. However, in the nanoindentation method, the relationshipbetween the indentation load and the indentation depth can be obtainedby automated and continuous measurement. Hence, unlike in the past,there are no individual differences between observers when visuallymeasuring deformation under an optical microscope, enabling the physicalproperties of the paint film to be evaluated to a high precision. Giventhat the paint film on the golf ball surface is strongly affected by theimpact of drivers and various other clubs and thus has a notinconsiderable influence on the golf ball properties, measuring the golfball paint film by the nanohardness test method and carrying out suchmeasurement to a higher precision than in the past is a very effectivemethod of evaluation.

When using the paint composition of the invention, a paint film layercan be formed on the surface of golf balls manufactured by a commonlyknown method, via the steps of preparing the paint composition at thetime of application, applying the composition to the golf ball surfaceby a conventional painting operation, and drying. The painting method isnot particularly limited. For example, suitable use can be made of spraypainting, electrostatic painting or dipping.

As described above, the golf ball paint composition of the inventionuses a polyester polyol as the base resin and a polyisocyanate as thecuring agent. Depending on the painting conditions, various types oforganic solvents may be mixed together. Examples of such organicsolvents include aromatic solvents such as toluene, xylene andethylbenzene; ester solvents such as ethyl acetate, butyl acetate,propylene glycol methyl ether acetate and propylene glycol methyl etherpropionate; ketone solvents such as acetone, methyl ethyl ketone, methylisobutyl ketone and cyclohexanone; ether solvents such as diethyleneglycol dimethyl ether, diethylene glycol diethyl ether and dipropyleneglycol dimethyl ether; alicyclic hydrocarbon solvents such ascyclohexane, methyl cyclohexane and ethyl cyclohexane; and petroleumhydrocarbon solvents such as mineral spirits.

The drying step may be similar to that for known two-part curingurethane paints. For the paint composition of the invention, the dryingtemperature may be set to at least about 40° C., and especially between40 and 60° C., and the drying time may be set to from 20 to 90 minutes,and especially from 40 to 50 minutes.

The thickness of the paint film layer, although not particularlylimited, is typically from 3 to 50 μm, and preferably from 5 to 20 μm.

The paint composition may be used on any type of golf ball, includingone-piece golf balls, two-piece solid golf balls having a core and acover encasing the core, and multi-piece solid golf balls having a coreof at least one layer and a multilayer cover encasing the core.

In a second aspect, the present invention is directed to a golf ballhaving a core, a cover positioned outside of the core, and a paint filmlayer positioned outside of the cover wherein the paint film layer isformed of the paint composition as described above.

The cover is the part of the ball that encases the core. Examplesinclude covers having at least one layer, including two-layer covers andthree-layer covers. In the case of a two-layer cover, the inner layer iscalled the “intermediate layer” and the outer layer is called the“outermost layer.” In the case of a three-layer cover, the respectivelayers are referred to as, in order from the inside, the “envelopelayer,” the “intermediate layer” and the “outermost layer.” The outsidesurface of the outermost layer typically has numerous dimples formedthereon for the purpose of enhancing the aerodynamic properties.

The materials making up the various layers of the cover are notparticularly limited. These may be formed of, e.g., ionomer resins,polyester resins, polyamide resins, and also polyurethane resins. Forexample, the intermediate layer may be formed of an ionomer resin or ahighly neutralized ionomer resin, and the outermost layer may be formedof a polyurethane resin.

It is preferable that a cover composition forming the cover has anelastic work recovery of at least 35%, preferably 43%. The elastic workrecovery is one parameter of the nanoindentation method for evaluatingthe physical properties of the cover material, which are almost similarexplanation as an elastic work recovery of the paint films as describedabove.

As to the elastic work recovery of the cover, letting an elastic workrecovery of the paint film be W1 and letting an elastic work recovery ofthe cover be W2, the difference W1−W2 between the elastic work recoveryof the paint film and the elastic work recovery of the cover ispreferable at most 40%, more preferably at most 30%.

The core may be formed using a known rubber material as the basematerial. A known base rubber such as a natural rubber or a syntheticrubber may be used as the base rubber. More specifically, the use ofprimarily polybutadiene, especially cis-1,4-polybutadiene having a cisstructure content of at least 40%, is recommended. Where desired, anatural rubber, polyisoprene rubber, styrene-butadiene rubber or thelike may be used in the base rubber together with the abovepolybutadiene. The polybutadiene may be synthesized with atitanium-based, cobalt-based, nickel-based or neodymium-based Zieglercatalyst or with a metal catalyst such as cobalt or nickel.

Co-crosslinking agents such as an unsaturated carboxylic acid or a metalsalt thereof, inorganic fillers such as zinc oxide, barium sulfate orcalcium carbonate, and organic peroxides such as dicumyl peroxide or1,1-bis(t-butylperoxy)cyclohexane may be compounded with the baserubber. In addition, where necessary, other ingredients such ascommercial antioxidants may be suitably added.

The paint film formed using the above paint composition thus has anexcellent abrasion resistance and moreover is able to enhance theperformance of golf balls, such as by preventing a marked decline in thespin performance of balls that have been coated with the paintcomposition, even when the balls are repeatedly struck with golf clubs.

EXAMPLES

Synthesis Examples, Working Examples of the invention and ComparativeExamples are given below by way of illustration, although the inventionis not limited by these Examples.

Working Examples 1 to 3, Comparative Examples 1 and 2

A core-forming rubber composition formulated as shown in Table 1 wasprepared and then cured and molded at 155° C. for 15 minutes, therebyproducing cores having a to diameter of 36.3 mm. Next, the cover layers(these being, in order from the inside: an envelope layer, anintermediate layer and an outermost layer) formulated of the resinmaterials shown in the same table were successively injection-moldedover the core.

The envelope layer had a thickness of 1.3 mm and a material hardness,expressed in terms of the Shore D hardness, of 52. The intermediatelayer had a thickness of 1.1 mm and a material hardness, in terms of theShore D hardness, of 62. The outermost layer had a thickness of 0.8 mmand a material hardness, in terms of the Shore D hardness, of 47. Whenthe outermost layer was injection molded, numerous dimples were formedat the same time on the outside surface of this layer.

TABLE 1 Golf ball parts Ingredients Amounts Cover Outermost T-8290 75layer T-8283 25 Hytrel 4001 11 Titanium oxide 3.9 Polyethylene wax 1.2Isocyanate compound 7.5 Intermediate Himilan 1605 50 layer Himilan 155715 Himilan 1706 35 Trimethylolpropane 1.1 Envelope layer HPF 1000 100Core Polybutadiene A 80 Polybutadiene B 20 Organic peroxide 1 Bariumsulfate 9 Zinc oxide 4 Zinc acrylate 43 Water 1.0 Zinc salt ofpentachlorothiophenol 0.3

Details on the above core materials are given below. Numbers in thetables indicate parts by weight.

-   Polybutadiene A: Available under the trade name “BR 01” from JSR    Corporation-   Polybutadiene B: Available under the trade name “BR 51” from JSR    Corporation-   Organic peroxide: Dicumyl peroxide, available under the trade name    “Percumyl D” from NOF Corporation-   Barium sulfate: Available under the trade name “Barico #100” from    Hakusui Tech-   Zinc oxide: Available under the trade name “Zinc Oxide Grade 3” from    Sakai Chemical Co., Ltd.-   Zinc acrylate: Available from Nippon Shokubai Co., Ltd.-   Water: Distilled water, from Wako Pure Chemical Industries, Ltd.-   Zinc salt of pentachlorothiophenol: Available from Wako Pure    Chemical Industries, Ltd.

Details on the cover (envelope layer, intermediate layer, and outermostlayer) materials are given below. Numbers in Table 1 indicate parts byweight.

-   HPF 1000: An ionomer available from E.I. DuPont de Nemours & Co.-   Himilan® 1605: A sodium-based ionomer available from DuPont-Mitsui    Polychemicals Co., Ltd.-   Himilan® 1557: A zinc-based ionomer available from DuPont-Mitsui    Polychemicals Co., Ltd.-   Himilan® 1706: A zinc-based ionomer available from DuPont-Mitsui    Polychemicals Co., Ltd.-   T-8290, T-8283: MDI-PTMG type thermoplastic polyurethanes available    from DIC Bayer Polymer under the trademark Pandex.-   Hytrel 4001: A polyester elastomer available from DuPont-Toray Co.,    Ltd.-   Polyethylene wax: “Sanwax 161P” from Sanyo Chemical Industries, Ltd.-   Titanium oxide: Tipaque R680, available from Ishihara Sangyo Kaisha,    Ltd.-   Isocyanate compound: 4,4′-Diphenylmethane diisocyanate

Formation of Paint Film Layer

Next, in each Example, the paint formulated as shown in Table 2 belowwas coated with an air spray gun onto the surface of the outermost layeron which numerous dimples had been formed, thereby producing golf ballshaving a 15 μm thick paint film layer formed thereon.

Elastic Work Recovery

The elastic work recovery of the paint was measured using a paint filmsheet having a thickness of 50 μm. The ENT-2100 nanohardness tester fromErionix Inc. was used as the measurement apparatus, and the measurementconditions were as follows.

-   -   Indenter: Berkovich indenter (material: diamond; angle α:        65.03°)    -   Load F: 0.2 mN    -   Loading time: 10 seconds    -   Holding time: 1 second    -   Unloading time: 10 seconds

The elastic work recovery was calculated as follows, based on theindentation work W_(elast) (Nm) due to spring-back deformation of thepaint film and on the mechanical indentation work W_(total) (Nm).

Elastic work recovery=W _(elast) /W _(total)×100(%)

TABLE 2 Working Example Comparative Example 1 2 3 1 2 Paint BasePolyester polyol (A) 23 25 26   27.5 27 formulation resin Polyesterpolyol (B) 15  8  4 —  3 (pbw) Organic solvent 62 67 70   72.5 70 (Totalcontent) (100)  (100)  (100)  (100)  (100)  Molecular weight of 16,500/19,400/ 21,800/ 25,600/ 22,050/ overall base resin (Mw/Mn) 1,300 1,5601,850 2,400 1,900 Curing Isocyanurate of HMDI 42 42 42 42 42 agentOrganic solvent 58 58 58 58 58 (Total content) (100)  (100)  (100) (100)  (100)  Molar compounding ratio    0.89    0.74    0.65    0.57   0.48 (NCO/OH) Properties Elastic work recovery (%) 84 80 77 62 64Film thickness (μm) 50 50 50 50 50

Synthesis of Polyester Polyol (A)

A reactor equipped with a reflux condenser, a dropping funnel, a gasinlet and a thermometer was charged with 140 parts by weight oftrimethylolpropane, 95 parts by weight of ethylene glycol, 157 parts byweight of adipic acid and 58 parts by weight of1,4-cyclohexanedimethanol, following which the temperature was raised to200 to 240° C. under stirring and the reaction was effected by continuedheating and stirring for 5 hours. This yielded polyester polyol (A)having an acid value of 4, a hydroxyl value of 170 and a weight-averagemolecular weight (Mw) of 28,000.

Next, the Polyester Polyol (A) synthesized above was dissolved in butylacetate, thereby preparing a varnish having a nonvolatile content of 70wt %.

In Working Example 1, a base resin was prepared by mixing 15 parts byweight of Polyester Polyol (B) (a saturated aliphatic polyester polyolavailable as “NIPPOLAN 800” from Tosoh Corporation; weight-averagemolecular weight (Mw), 1,000; 100% solids) and an organic solventtogether with 23 parts by weight of the above Polyester Polyol (A)solution. The resulting mixture had a nonvolatile content of 38.0 wt %.

In Working Example 2, a base resin was prepared by mixing 8 parts byweight of Polyester Polyol (B) (“NIPPOLAN 800” from Tosoh Corporation;100% solids) and an organic solvent together with 25 parts by weight ofthe above Polyester Polyol (A) solution. The resulting mixture had anonvolatile content of 33.0 wt %.

In Working Example 3, a base resin was prepared by mixing 4 parts byweight of Polyester Polyol (B) (“NIPPOLAN 800” from Tosoh Corporation;100% solids) and an organic solvent together with 26 parts by weight ofthe above Polyester Polyol (A) solution. The resulting mixture had anonvolatile content of 30.0 wt %.

In Comparative Example 1, a base resin was prepared by, as shown inTable 2, dissolving Polyester Polyol (A) alone in butyl acetate withoutmixing in the above Polyester Polyol (A) solution. The resultingsolution had a nonvolatile content of 27.5 wt %.

In Comparative Example 2, a base resin was prepared by mixing 3 parts byweight of Polyester Polyol (B) (“NIPPOLAN 800” from Tosoh Corporation;100% solids) and an organic solvent together with 27 parts by weight ofthe above Polyester Polyol (A) solution. The resulting mixture had anonvolatile content of 30.0 wt %.

Measurement of Molecular Weights (Mw and Mn)

The molecular weights were measured using the following apparatus.

-   -   Apparatus: HLC-8220, a high-speed gel permeation chromatography        system from Tosoh Corporation    -   Columns: two coupled columns        -   TSK-GEL G2000H_(XL) and TSK-GEL G4000H_(XL)    -   Column Temperature: 40° C.    -   Detector: differential refractometer    -   Eluant: THF    -   Column flow rate: 0.6 mL/min

Next, the curing agent shown in Table 2 was dissolved in an organicsolvent and used. That is, the isocyanurate of HMDI (Duranate™ TPA-100from Asahi Kasei Corporation; NCO content, 23.1%; 100% nonvolatiles)and, as organic solvents, ethyl acetate and butyl acetate, were added inthe proportions shown in Table 2, thereby preparing the paint.

The golf balls obtained in the respective Working Examples andComparative Examples were evaluated according to the criteria describedbelow for paint film appearance. The results are shown in Table 3.

Evaluation of Ball Surface Appearance after Sand Abrasion Test

A pot mill with an outside diameter of 210 mm was charged with about 4kg of sand having a size of about 5 mm, and 15 golf balls were placed inthe mill. The balls were agitated in the mill at a speed of about 50 to60 rpm for 120 minutes, following which the balls were removed from themill and the appearance of each ball was rated according to thefollowing criteria.

Rating Criteria

-   -   Exc: Ball surface is free of conspicuous peeling, blemishes,        etc.    -   Good: Minor scratches and blemishes are visible on ball surface    -   NG: Large peeling due to abrasion, or blemishes and diminished        gloss are conspicuous on ball surface.

Evaluation of Ball Surface Appearance After Sand/Water Abrasion Test

A pot mill with an outside diameter of 210 mm was charged with about 4kg of sand having a size of about 5 mm and water, and 15 golf balls wereplaced in the mill. The balls were agitated in the mill at a speed ofabout 50 to 60 rpm for 120 minutes, following which the balls wereremoved from the mill and the appearance of each ball was ratedaccording to the following criteria.

Rating Criteria

-   -   Exc: Ball surface is free of conspicuous peeling, blemishes,        etc.    -   Good: Minor scratches and blemishes are visible on ball surface    -   NG: Large peeling due to abrasion, or blemishes and diminished        gloss are conspicuous on ball surface.

TABLE 3 Working Example Comparative Example 1 2 3 1 2 Ball propertiesSand abrasion test Exc Exc Good NG NG Sand/Water abrasion test Good GoodGood Good Good

The golf ball property results shown in Table 3 demonstrate thefollowing.

The results from the sand abrasion test and the sand/water abrasion testcarried out on the golf balls in Working Examples 1 to 3 according tothe invention were all good, indicating that these balls had a goodpaint film appearance.

By contrast, in Comparative Examples 1 and 2, the ball surface followingthe sand/water abrasion test was good, but peeling due to abrasion,blemishes, diminished gloss, etc. were conspicuous on the ball surfacefollowing the sand abrasion test.

Working Examples 4 to 8 and Comparative Examples 3 to 5

A core-forming rubber composition formulated as shown in above Table 1was prepared and then cured and molded at 155° C. for 15 minutes,thereby producing cores having a diameter of 36.3 mm. Next, the coverlayers (these being, in order from the inside: an envelope layer, and anintermediate layer) formulated of the resin materials shown in the sametable were successively injection-molded over the core. The envelopelayer had a thickness of 1.3 mm and a material hardness, expressed interms of the Shore D hardness, of 52. The intermediate layer had athickness of 1.1 mm and a material hardness, in terms of the Shore Dhardness, of 62.

As to an outermost layer, the composition formulated as shown in thefollowing Table 4 was prepared. The outermost layer had a thickness of0.8 mm and a material hardness, in terms of the Shore D hardness, of 47(I), 43 (II), 56 (III) and 63 (IV) respectively. When the outermostlayer was injection molded, numerous dimples were formed at the sametime on the outside surface of this layer.

TABLE 4 Resin materials (pbw) I II III IV TPU1 100 TPU2 100 AN 4319 25Himilan 1605 50 Himilan 1601 37.5 Himilan 1557 37.5 AM 7329 50 Shore Dhardness 47 43 56 63

It is noted that additives are formulated in an appropriate amount ineach of the above compositions.

Trade names for the materials in the table are indicated below.

TPU1: An aromatic ether-type thermoplastic polyurethane (Shore Dhardness, 47) available under the trade name “Pandex” from DIC CovestroPolymer.TPU2: An aromatic ether-type thermoplastic polyurethane (Shore Dhardness, 43) available under the trade name “Pandex” from DIC CovestroPolymer.AN4319: Available from Dow-Mitsui Polychemicals Co., Ltd. under thetrademark Nucrel®.Himilan 1605, Himilan 1601, Himilan 1557: Ionomers available fromDow-Mitsui Polychemicals Co., Ltd.AM 7329: Ionomers available from Dow-Mitsui Polychemicals Co., Ltd.

Elastic Work Recovery of Golf Ball Cover

The elastic work recovery of the cover of the golf ball was measuredusing a golf ball itself non-coated by a paint film as a sample. NanoIndenter G200 from Toyo Corporation was used as the measurementapparatus, and the measurement conditions were as follows.

-   -   Indenter: Berkovich indenter (angle α: 130.06°)    -   Load F: 100 mN    -   Loading time: 15 seconds    -   Holding time: 20 second    -   Unloading time: 15 seconds

The elastic work recovery was calculated as follows, based on theindentation work W_(elast) (Nm) due to spring-back deformation of thecover of the golf ball and on the mechanical indentation work W_(total)(Nm).

Elastic work recovery=W _(elast) /W _(total)×100(%)

Next, in each Example, the paint formulated as shown in Table 5 belowwas coated with an air spray gun onto the surface of the outermost layeron which numerous dimples had been formed, thereby producing golf ballshaving a 15 nm thick paint film layer formed thereon.

TABLE 5 Working Example Comparative Example 4 5 6 7 8 3 4 5 Paint BasePolyester polyol (A)   27.5 27.5 27.5 27.5 27.5 27.5 27.5 27.5formulation resin Polyester polyol (B) — — — — — — — — (pbw) Organicsolvent   72.5 72.5 72.5 72.5 72.5 72.5 72.5 72.5 (Total content) (100) (100)   (100)   (100)   (100)   (100)   (100)   (100)   Molecular weightof 25.600/ 25,600/ 25,600/ 25,600/ 25,600/ 25,600/ 25,600/ 25,600/overall base resin (Mw/Mn) 2,400 2,400 2,400 2,400 2,400 2,400 2,4002,400 Curing Isocyanurate of   42.1 38.6 30.5 42.1 42.1 30.5 30.5 42.0agent HMDI Adducts of HMDI   4.7 12.9 30.5  4.7  4.7 30.5 30.5 — Organicsolvent   53.2 48.5 39.0 53.2 53.2 39.0 39.0 58.0 (Total content) (100) (100)   (100)   (100)   (100)   (100)   (100)   (100)   Compoundingweight ratio 90/10 75/25 50/ 90/ 90/ 50/ 50/ 100/ (Isocyanurate/Adducts)50 10 10 50 10 0 Properties Elastic work recovery W1 (%) 80 85   90  80   80   90   90   62   Film thickness (μm) 50 50   50   50   50   50  50   50   Outermost Types I I I II III IV III I cover Elastic workrecovery W2 (%) 44 44   44   52   35   30   35   44   Difference W1 − W2of Elastic work recovery (%) 36 41   46   28   45   60   55   18  

Elastic Work Recovery of Paint Film

The elastic work recovery of the paint is the same content as the abovemeasurement of Working Examples 1 to 3 & Comparative Examples 1 and 2 asdescribed above.

In Working Examples 4 to 8 & Comparative Examples 1 to 3, a base resinwas prepared by, as shown in Table 5, dissolving Polyester Polyol (A)alone in butyl acetate without mixing in the above Polyester Polyol (A)solution. The resulting solution had a nonvolatile content of 27.5 wt %.It is noted in Table 5 that the Polyester Polyol (A) is the same asExamples using the above Table 2.

Next, the isocyanurate of HMDI (Duranate™ TPA-100 from Asahi KaseiCorporation; NCO content, 23.1%; 100% nonvolatiles, which is the same asthe isocyanurate of HMDI of Table 2) and the adduct of HMDI (Duranate™E402-80B″ from Asahi Kasei Corporation; NCO content, 7.6%; 80%nonvolatiles), and, as organic solvents, ethyl acetate and butylacetate, were added in the proportions shown in Table 5, therebypreparing the paint.

The golf balls obtained in the respective Working Examples andComparative Examples were evaluated according to the criteria for paintfilm appearance described above (i.e. the same criteria as WorkingExamples 1 to 3 & Comparative Examples 1 and 2).

TABLE 6 Working Example Comparative Example 4 5 6 7 8 3 4 5 Ball Sandabrasion test Good Exc Exc Exc Good Good Good NG properties Sand/Waterabrasion test Good Good Good Good Good NG NG Good

Japanese Patent Application No. 2016-225966 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A golf ball paint composition comprising a urethane paint containingpolyol as a base resin and polyisocyanate as a curing agent, wherein thepolyisocyanate includes two types of isocyanurate and adduct ofhexamethylene diisocyanate and the composition has an elastic workrecovery of at least 70%.
 2. The paint composition of claim 1, whereinthe composition has an elastic work recovery of at least 80%.
 3. Thepaint composition of claim 1, wherein the compounding ratio by weightratio of the isocyanurate (A) to the adduct (B) of hexamethylenediisocyanate, expressed as (A)/(B), is from 95/5 to 40/60.
 4. The paintcomposition of claim 1, wherein the polyol includes one or two types ofpolyester polyol.
 5. A golf ball having a core, a cover positionedoutside of the core, and a paint film layer positioned outside of thecover wherein the paint film layer is formed of the paint composition ofclaim
 1. 6. The golf ball of claim 1, wherein a cover compositionforming the cover has an elastic work recovery of at least 35%.
 7. Thegolf ball of claim 1, wherein letting an elastic work recovery of thepaint film be W1 and letting an elastic work recovery of the cover beW2, the difference W1−W2 between the elastic work recovery of the paintfilm and the elastic work recovery of the cover is at most 40%.